DESCRIPTION: Most of our knowledge concerning B-lymphopoiesis is derived from murine long-term bone marrow cultures. This system has helped to understand some of the molecules and mechanisms that regulate the survival, growth and differentiation of lymphoid cells. Development of a corresponding system for studying human B-lymphopoiesis has been a challenge but the applicants and others have recently devised in vitro culture systems to propagate normal B-cell progenitors or B-lineage precursors from patients with acute lymphoblastic leukemia. It was found that either of these cell types when cultivated by themselves rapidly die by apoptosis, but when grown on a feeder layer of allogeneic bone marrow stromal fibroblasts, they live for several months with the leukemic cells surviving longer. The applicant studies thus far suggest that a physical interaction of normal and leukemic progenitors to the stromal fibroblasts is essential for their survival and that leukemic cells are less stringent in their growth and survival requirement than their normal counterparts. Thus, the leukemic cells provide a convenient model system in vitro to study the molecules that are essential for their growth and survival. The long-term goal is to identify these molecules and the mechanism of their action. The specific aims are to identify the molecules involved in the adhesive interactions between leukemic lymphoblasts and fibroblasts by immunoelectron microscopy and to elucidate the receptor-ligand interactions that are essential for their survival and growth as determined by examining the effects of specific antibodies on lymphoblast/fibroblast cultures. These studies are relevant to cancer problem in two ways. First, the information obtained from this study could be used to optimize the survival and growth conditions of lymphoblasts from ALL patients. Such an optimized culture system could be used to study the effects of drugs on patient samples to detect interpatient variability in drug sensitivity and to identify effective anti-leukemic agents. Second, studies by the applicant and others suggest that pseudodiploid ALL blasts and leukemic myeloblasts that cause aggressive disease in vivo grow well in vitro whereas hyperdiploid ALL blasts that are associated with a favorable prognosis of the disease grow poorly in vitro. Thus the growth characteristics of the leukemic blasts, especially under optimal conditions, may provide valuable information concerning the outcome of therapy. Additionally, the above studies may help elucidate some of the complex cellular and molecular interactions that regulate normal human B-cell development. Therefore, the proposed research could yield valuable basic information on normal B-lymphopoiesis as well as leukemogenic events.